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Remote Entanglement of Two Single Atoms

Carolin Hahn

Published Jan 1, 2014• 0 citations
OpenAlex

Abstract

This thesis reports on the generation of entanglement between two single atoms, located in different laboratories at a distance of 21 m. The entanglement is established in the conceptually most fundamental way - by exchange of a single photon. To this end, we efficiently create high-fidelity entanglement between one of the atoms and a photon, and then faithfully map the entanglement onto the other atom. Both the photon emission and absorption process are facilitated by employing high-finesse optical resonators that strongly enhance the coupling between light and matter.

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This thesis reports on the generation of entanglement between two single atoms, located
in different laboratories at a distance of 21 m. The entanglement is established in the
conceptually most fundamental way - by exchange of a single photon. To this end, we efficiently create high-fidelity entanglement between one of the atoms and a photon, and then faithfully map the entanglement onto the other atom. Both the photon emission and absorption process are facilitated by employing high-finesse optical resonators that strongly enhance the coupling between light and matter.
Entanglement has been recognised as a puzzling yet central element of quantum physics. While photons serve as flying qubits to distribute entanglement, the entanglement of stationary qubits at remote sites is a key resource for envisioned applications like distributed quantum computing. In our experiment we create remote entanglement between a single atom located inside a high-finesse optical cavity and a Bose-Einstein condensate (BEC). To this end we generate a single photon in the atom-cavity system, entangling the photon polarisation with the atomic Zeeman state. The photon is transported to a different laboratory in an optical fiber, where it is stored in a BEC employing electromagnetically induced transparency (EIT). This converts the atom-photon entanglement into remote matter-matter entanglement. Subsequently we map the matter-matter entanglement onto photon-photon entanglement. The experimental setup is sketched in Fig. 1.
We report observations of entanglement of two remote atomic qubits, achieved by generating an entangled state of an atomic qubit and a single photon at site , transmitting the photon to site in an adjacent laboratory through an optical fiber, and converting the photon into an atomic qubit. Entanglement of the two remote atomic qubits is inferred by performing, locally, quantum state transfer of each of the atomic qubits onto a photonic qubit and subsequent measurement of polarization correlations in violation of the Bell inequality [EQUATION: SEE TEXT]. We experimentally determine [EQUATION: SEE TEXT]. Entanglement of two remote atomic qubits, each qubit consisting of two independent spin wave excitations, and reversible, coherent transfer of entanglement between matter and light represent important advances in quantum information science.
Entanglement between stationary systems at remote locations is a key resource for quantum networks. We report on the experimental generation of remote entanglement between a single atom inside an optical cavity and a Bose-Einstein condensate (BEC). To produce this, a single photon is created in the atom-cavity system, thereby generating atom-photon entanglement. The photon is transported to the BEC and converted into a collective excitation in the BEC, thus establishing matter-matter entanglement. After a variable delay, this entanglement is converted into photon-photon entanglement. The matter-matter entanglement lifetime of 100 μs exceeds the photon duration by 2 orders of magnitude. The total fidelity of all concatenated operations is 95%. This hybrid system opens up promising perspectives in the field of quantum information.
Entanglement between a single photon and a matter qubit is an indispensable resource for quantum repeater and quantum networks. With atomic ensembles, the entanglement creation probability is typically very low to inhibit high-order events. In this paper, we propose and experimentally realize a scheme that creates atom-photon entanglement with an intrinsic efficiency of 50%. We make use of Rydberg blockade to generate two collective excitations, lying in separate internal states. By introducing the momentum degree of freedom for the excitations, and interfering them via Raman coupling, we entangle the two excitations. Via retrieving one excitation, we create the entanglement between the polarization of a single photon and the momentum of the remaining atomic excitation, with a measured fidelity of 0.901(8). The retrieved optical field is verified to be genuine single photons. The realized entanglement may be employed to create entanglement between two distant nodes in a fully heralded way and with a much higher efficiency.
Entanglement distributed over a set of individually addressable qubit nodes is the enabling resource for a plethora of applications ranging from tests of quantum physics to secure and modular quantum information networks. Entanglement between two memory qubits has been realized on various platforms, but extension to more nodes remains rare and formidably challenging. The principal bottleneck is the efficiency of the light-matter interfaces connecting the qubit nodes to their communication channels. Here, we efficiently generate, distribute and store a three-qubit entangled state across three independent laboratories containing single atoms coupled to optical resonators. We sequentially entangle the atoms pairwise, two by heralded photonic entanglement swapping and two by heralded state transfer. We reach a three-qubit entanglement fidelity of 77(1)% and an entanglement lifetime above 200us. The observed qubit correlations violate Mermin's inequality while closing the detection loophole. Our three-qubit entanglement-generation efficiency is 0.16%. This unprecedented efficiency of our scheme establishes a clear route towards multi-node quantum networks.